Road Performance And Engineering Application Of Soda Residue-Phosphate Tailings-Clay Admixtures

In recent years,Lianyungang City has subjected to many problems in urban development.Particularly,the land occupation and environmental pollution originated by the accumulation of soda residue and phosphate tailing are more prominent.In this context,numerous road construction/widen projects in Lianyungang are listed in the 13th five-year plan of Jiangsu province,leading to an urgent need of gravel soil to serve as filling materials.However,Lianyungang has banned the mining of local gravel soil,with the country’s attention to the ecological environment year by year.Hence,may road projects have to extend the construction period due to a lack of fillers,which took time and energy to buy from other provinces.To tackle this issue,previous researches and engineering practices have found that if the phosphate tailing is mixed with Lianyungang coastal soft clay,the grading of the mixture will be improved,the dense structure is formed,in which tailing act as a skeleton while clay as fillings.On this basis,soda residue is added.Ca SO₄,Ca（OH）₂ and other components of soda residue are used to react with clay and tailings to form cementitious materials,which can further improve the strength performance of the mixture.Based on this framework,the mixing ratio is set with soda residue and clay content as variables.And then the corresponding mechanical properties,road performance,microscopic mechanism and field tests were carried out to explore suitable mix ratio of soda residue-phosphate tailing-clay mixed packing to meet the roadbed requirement.The following conclusions can be drawn.（1）The basic physical and mechanical properties,chemical composition and micro-morphology of raw material soda residue,phosphate tailings,and clay are systematically analyzed;（2）By changing the fraction of soda residue and clay in the mixture,five groups of materials named as clay modified phosphate tailings,soda residue modified phosphate tailings,soda residue modified clay,soda residue-phosphorus tailings-clay,and lime treated clay（contrast group）are formed.The compaction test,CBR test,and 7d unconfined compressive strength test were performed,and the characterization of the effects of soda residue,tailings,clay,and lime content on the compaction and strength properties of the material were put forward.Finally,an efficient mix ratio is selected among the groups of clay modified tailings,soda residue modified clays,soda residue-tailed sands-clays,and lime modified clays.（3）The gradation analysis,resilience modulus,water stability,dry-wet cycle,compaction degree and other road performance tests were performed for the selected excellent mix ratio.The impacts of the soaking age,dry-wet cycle number and changes in compaction on its road performance were analyzed.The results show that even under the worst conditions such as long-term water soaking,dry-wet cycle,and compaction change,the proposed soda residue-tailed sands-clays mixture can still maintain or even exceed the behavior as compared to traditional lime soil.（4）Electron microscopy scanning is carried out on the soda residue modified clay,and the micro-morphology and products were observed.It is found that the clay particles in the mixture filled the pores of soda residue.Compared with the original soda residue,the new structure is more dense.Combined with the existing results,product morphology and EDS test,it is determined that the soda-residue modified clay mainly produced cemented substances such as hydrated calcium silicate（CSH）and ettringite（AFt）which have a gelling effect on the mixture particles.（5）The degree of compaction,load-bearing ratio（CBR）,and modulus of resilience were selected as evaluation indicators.a field test section of a highway in Lianyungang is carried out.The construction technology of the filling is summarized,the economic and social benefits of the filling is evaluated.